LHC Accelerator Status and PlansEric Prebys, FermilabDirector, US LHC Accelerator Research Program (LARP)
Google welcome screen from September 10, 2008
1/5/2010
Outline Overview of the LHC 2008 Startup and “The Incident” The Response Startup and current commissioning status 2009/2010 Run plans The future (as time permits)
Note: This talk is a monument to plagiarism. I’ll give specific acknowledgements and “further reading” at the end.
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LHC Layout
8 crossing interaction points (IP’s) Accelerator sectors labeled by which points they go between
ie, sector 3-4 goes from point 3 to point 41/5/2010 3Eric Prebys - LHC Talk, Aspen 2010
CERN experiments Huge, general purpose experiments:
“Medium” special purpose experiments:Compact Muon Solenoid (CMS) A Toroidal LHC ApparatuS (ATLAS)
A Large Ion Collider Experiment (ALICE) B physics at the LHC (LHCb)
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Nominal LHC parameters compared to Tevatron
Parameter Tevatron “nominal” LHC
Circumference 6.28 km (2*PI) 27 kmBeam Energy 980 GeV 7 TeVNumber of bunches 36 2808Protons/bunch 275x109 115x109
pBar/bunch 80x109 -Stored beam energy 1.6 + .5 MJ 366+366 MJ*Peak luminosity 3.3x1032 cm-2s-1 1.0x1034 cm-2s-1
Main Dipoles 780 1232Bend Field 4.2 T 8.3 TMain Quadrupoles ~200 ~600Operating temperature 4.2 K (liquid He) 1.9K (superfluid
He)*2.1 MJ ≡ “stick of dynamite” very scary numbers
1.0x1034 cm-2s-1 ~ 50-100 fb-1/yr
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LHC (partial) timeline 1994:
The CERN Council formally approves the LHC 1995:
LHC Technical Design Report complete 2000:
LEP completes its final run 2002:
Magnet production fully transferred to industry 2005
Civil engineering complete (CMS cavern) First dipole lowered into tunnel
2007 Last magnet delivered All interconnections completed
2008 Accelerator complete Last public access Ring cold and under vacuum
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Problems Discovered Prior to 2008 Start
For these reasons, the initial energy target was reduced to 5+5 TeV well before the start of the 2008 run.
Magnet de-training ALL magnets were trained to
achieve 7+ TeV after a thermal cycle.
After being installed in the tunnel, it was discovered that the magnets supplied by one of the three vendors “forgot” their training, and would need to be retrained to reach 7 TeV.
Symmetric Quenches The original LHC quench protection system subtracted the inductive
voltage drop by taking the difference between the voltage drop across the two apertures.
It was discovered in tests that when quenches propagate from one dipole to the next, they often do so symmetrically, rendering the system dangerously insensitive at high current.
1st quench in tunnel
1st Training quench above ground
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Experimental reach of LHC vs. Tevatron
W (MW=80 GeV)Z (MZ=91 GeV)
200 pb-1 at 5 TeV+5 TeV~5 fb-1 at 1 TeV+ 1 TeV
Only HEP slide in this talk
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Sept 10, 2008: The (first) big day 9:35 – First beam injected 9:58 – beam past CMS to
point 6 dump 10:15 – beam to point 1
(ATLAS) 10:26 – First turn! …and there was much
rejoicing
Commissioning proceeded smoothly and rapidly until September 19th, when something very bad happened
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Nature abhors a (news) vacuum… Italian newspapers were very poetic (at least as
translated by “Babel Fish”):"the black cloud of the bitterness still has not
been dissolved on the small forest in which they are dipped the candid buildings of the CERN"
“Lyn Evans, head of the plan, support that it was better to wait for before igniting themachine and making the verifications of the parts.“*
Or you could Google “What really happened at CERN”:
* “Big Bang, il test bloccato fino all primavera 2009”, Corriere dela Sera, Sept. 24, 2008
**
**http://www.rense.com/general83/IncidentatCERN.pdf1/5/2010 10Eric Prebys - LHC Talk, Aspen 2010
What (really) really happened on September 19th* Sector 3-4 was being ramped to 9.3 kA, the equivalent of 5.5
TeV All other sectors had already been ramped to this level Sector 3-4 had previously only been ramped to 7 kA (4.1 TeV)
At 11:18AM, a quench developed in the splice between dipole C24 and quadrupole Q24 Not initially detected by quench protection circuit Power supply tripped at .46 sec Discharge switches activated at .86 sec
Within the first second, an arc formed at the site of the quench The heat of the arc caused Helium to boil. The pressure rose beyond .13 MPa and ruptured into the insulation
vacuum. Vacuum also degraded in the beam pipe
The pressure at the vacuum barrier reached ~10 bar (design value 1.5 bar). The force was transferred to the magnet stands, which broke.*Official talk by Philippe LeBrun, Chamonix, Jan. 2009
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Pressure forces on SSS vacuum barrier
Vacuum
1/3 load on cold mass (and support post)~23 kN
1/3 load on barrier~46 kN
Pressure1 bar
Total load on 1 jack ~70 kN V. Parma
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Collateral damage: magnet displacements
QQBI.27R3
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Collateral damage: magnet displacements
QQBI.27R3V2 line
QQBI.27R3N line
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Collateral damage: magnet displacements
QBBI.B31R3Extension by 73 mm
QBQI.27R3Bellows torn open
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Collateral damage: secondary arcs
QQBI.27R3 M3 line
QBBI.B31R3 M3 line
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Collateral damage: ground supports
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Collateral damage: Beam Vacuum
LSS3 LSS4
Beam Screen (BS) : The red color is characteristic of a clean copper
surface
BS with some contamination by super-isolation (MLI multi layer
insulation)
BS with soot contamination. The grey color varies depending on the thickness of the soot, from grey to
dark.
OKDebris
MLISoot
The beam pipes were polluted with thousands of
pieces of MLI and soot, from one extremity to the other of
the sector
clean MLI sootArc burned through beam vacuum pipe
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15 Quadrupoles (MQ)1 not removed (Q19) 14 removed
8 cold mass revamped (old CM, partial de-cryostating for cleaning and careful inspection of supports and other components)
6 new cold masses Some additional old
cold masses salvageable
42 Dipoles (MBs)3 not removed
(A209,B20,C20)39 removed
9 Re-used (old cold mass, no decryostating –except one?)
30 new cold masses New cold masses are
much faster to prepare than rescuing doubtful dipoles)
Many old cold masses salvageable.
Replacement of magnets
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Important questions about Sept. 19 Why did the joint fail?
Inherent problems with joint design No clamps Details of joint design Solder used
Quality control problems Why wasn’t it detected in time?
There was indirect (calorimetric) evidence of an ohmic heat loss, but these data were not routinely monitored
The bus quench protection circuit had a threshold of 1V, a factor of >1000 too high to detect the quench in time.
Why did it do so much damage? The pressure relief system was designed around an MCI
Helium release of 2 kg/s, a factor of ten below what occurred.
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Theory: A resistive joint of about 220 n with bad electrical and thermal contacts with the stabilizer
No electrical contact between wedge and U-profile with the bus on at least 1 side of the
joint
No bonding at joint with the U-profile and the
wedge
A. Verweij
• Loss of clamping pressure on the joint, and between joint and stabilizer
• Degradation of transverse contact between superconducting cable and stabilizer
• Interruption of longitudinal electrical continuity in stabilizer
What happened?
Problem: this is where the evidence used to
be1/5/2010 21Eric Prebys - LHC Talk, Aspen 2010
Improved quench protection* Old quench protection circuit triggered at
1V on bus. New QPS triggers at .3 mV
Factor of 3000Should be sensitive down to 25 nOhms (thermal
runaway at 7 TeV)Can measure resistances to <1 nOhm
Concurrently installing improved quench protection for “symmetric quenches”A problem found before September 19th
Worrisome at >4 TeV*See talks by Arjan Verveij and Reiner Denz, Chamonix 2009
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Improved pressure relief*
2 kg/s
20 kg/s
40 kg/s
DP1
1.52
2.53
3.54
4.5
0 20 40 60 80 100 120
Vac
encl
osur
e P
[bar
]
Vac enclosure He T [K]
2 kg/s20 kg/s
40 kg/s
DP
11.11.21.31.41.51.6
0 20 40 60 80 100 120
Vac
encl
osur
e P
[bar
]
Vac enclosure He T [K]
New configuration on four cold sectors: Turn several existing flanges into pressure reliefs (while cold). Also reinforce stands to hold ~3 bar
New configuration on fourwarm sectors: new flanges(12 200mm relief flanges)
(DP: Design Pressure) L. Tavian
*Vittorio Parma and Ofelia Capatina, Chamonix 20091/5/2010 23Eric Prebys - LHC Talk, Aspen 2010
Bad surprise With new quench protection, it was determined that joints
would only fail if they had bad thermal and bad electrical contact, and how likely is that? Very, unfortunately must verify copper joint
Have to warm up to at least 80K to measure Copper integrity.
Solder used to solder joint had the same melting temperature as solder used to pot cable in stablizer Solder wicked away from cable
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Machine wide activities Q4 2008 and 2009
Electrical splice measurements everywhere while cold (measuring nΩ) Q4 2008 Had to warm up sectors 12 56 67
Electrical stabilizer measurements everywhere while warm or at 80K (measuring µΩ) Q1 Q2 2009 Had to warm up sector 45
Major new protection system based on electrical measurements Q1 – Q4 2009 (nQPS)
Pressure relief valves installed everywhere possible Q1 – Q3 2009 (dipoles have to be warm)
Reinforcement of floor anchors everywhere Q1 – Q3 2009
Q4 2008 Q1 2009 Q2 2009 Q3 2009 Q4 200912 Cold Cold Warm Warm Warm Cold Cold23 < 100K < 100K < 100K Cold Cold 80K Cold Cold
34 Warm Warm Warm Warm Cold Cold45 < 100K < 100K 80K Warm Warm Cold Cold56 Cold Cold Warm Warm Warm Cold Cold67 Cold Cold Warm Warm Warm Cold Cold78 Cold < 100K < 100K 80K 80K Cold Cold81 Cold < 100K < 100K 80K 80K Cold Cold
Q4 2008 Q1 2009 Q2 2009 Q3 2009 Q4 2009
Sector 34 repair Restart
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2009 Plans (as of November 1)*
Decision to limit energy to 1.2 TeV based on need for final shakedown of new quench protection system.
Somewhat ahead of this schedule
*Taken from slides by Roger Bailey, shown at LARP meeting
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November 20, 2009: Going around…again
Total time: 1:43 Then things began to move with dizzying speed…
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First Tune Measurement (within an hour)
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Beam 1 Captured about an hour after first turn!!
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November 23rd: First Collisions!
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Progress since start up Sunday, November 29th
Both beams accelerated to 1.18 TeV simultaneously Sunday, December 6th
Stable 4x4 collisions at 450 GeV Tuesday, December 8th
2x2 accelerated to 1.18 TeV First collisions seen in ATLAS before beam lost!
Monday, December 14th Stable 2x2 at 1.18 TeV Collisions in all four experiments 16x16 at 450 GeV
Wednesday, December 16th
4x4 to 1.18 TeV Squeeze to 7m Collisions in all four experiments 18:00 – 2009 run ended
>1 million events at 450x450 GeV 50,000 events at 1.18x1.18 TeV Merry Christmas – shutdown until Feb. 2010 to commission quench
protection
LHC Highest energy accelerator
LHC Highest energy collider
Should be good to 3.5 TeV after restart
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Commissioning*: 450 GeV RF
Excellent apart from some controls & procedural issues Measurement and control of key beam parameters
Orbit, tune, chromaticity, coupling, dispersion lifetime optimization: tune, chromaticity, orbit energy matching aperture
Optics checks beating & correction polarity checks of correctors and BPMs
*Courtesy Mike Lamont1/5/2010 33Eric Prebys - LHC Talk, Aspen 2010
Commissioning: Ramp and 1.18 TeV Ramp
2 beams to 1.2 TeV Feedback excellent, feed forward show good
reproducibility Squeeze
Some work required here but impressive nonetheless Collisions
steering, scans Two beam operation – with and without bumps Experiments’ magnets
Solenoids – brought on without fuss and corrected Dipoles – brought on at 450 GeV – issues with transfer
functions
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Commissioning (cont’d) Beam dump
extensive program of tests with beam Inject & dump, circulate & dump Beam based alignment of TCDQ and TCS Aperture scans Extraction tests Synchronization with abort gap Asynchronous beam dump tests with de-bunched beam
Collimation Full program of beam based positioning, hierarchy established and respected in tests collimation setup remained valid over 6 days, relying on orbit
reproducibility and optics stability Even the Roman pots got a run out
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Commissioning (cont’d) Beam Position Monitors (BPM’s)
looking very good, FIFO as per injection tests capture mode commissioned – enabling multi-turn acquisition and analysis
Beam Loss Monitors (BLM’s) magnificent following full deployment during injection tests – a close to full
operational tool issues with SEMs, some thresholds to be adjusted, some still masked
Beam Current Measurement (DBCT, FBCT, lifetime) commissioned and operational controls issues
Wire scanners operational, calibrated and giving reasonable numbers
Coupling measured and corrected
Abort Gap Monitor cleaning attempted with transverse damper
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Commissioning (cont’d) Tune
BBQ FFT from day 1 – used in feedback during ramp horizontal and vertical MKQA tune kicker for B1 and B2
operational PLL – good progress, feedback to be tested radial modulation tested issues with the hump, tune stability, 8 kHz
Chromaticity Standard method Semi-automatic BBQ peak analysis Radial modulation
Synchrotron light monitor B2: undulator commissioned, SLM operational at 450 GeV and 1.2
TeV B1: undulator not commissioned, SLM operational at 1.2
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Optics measurements: 450 GeV and 1.18 TeV
LHC BeamCommissioning
Team
Commissioning slides from talk by R. Assmann and F. Schmidt at recent Tevatron studies workshop
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Dec. 13, 2009: 24 hours running - currents
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Beam Dump with 16 BunchesKickers sweep bunches to “dilute” intensity on dump
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LHC Collimation Performance (Phase I System)
Could get to design intensity (at injection energy)
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Ramp 2 on 2 to 1.18 TeV: ~no Losses
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Tune Adjustments for Beam2
B1: Qx = 0.293, Qy = 0.269; lifetime = 26h
B2: Qx = 0.297, Qy = 0.267; lifetime = 5h
B1: Qx = 0.293, Qy = 0.269; lifetime = 25h
B2: Qx = 0.312, Qy = 0.305; lifetime = 12h
3/112/7
3/10
1/3
LHC BeamCommissioning
Team1/5/2010 46Eric Prebys - LHC Talk, Aspen 2010
Beam size measurements (blow up on beam 2)
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Beam Control at 1.18 TeV
Automated feedbacks seem to be working, but not quite yet standard operations.
Bottom line: things look good!
Position control
Bump introduced
Removed by feedback loop
Tune feedback
Feel happy that yellow line and pink line add up to blue line
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General Plan for 2010*
Decision whether to go above 3.5 TeV will be made next week at Chamonix Based on “confidence in
thermal model” 50/50 according to Mike
Lamont
1 month pilot & commissioning3 month 3.5 TeV
1 month to go up in energy (maybe)5 month 5 TeV1 month ions
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Understanding LHC Luminosity
RNNnfL
N
bbbrev*4
Total beam current. Limited by:• Uncontrolled beam loss!!• E-cloud and other
instabilities
*, limited by• magnet technology• chromatic effects
Brightness, limited by
• Injector chain• Max tune-shift
Geometric factor, related to crossing angle…
*see, eg, F. Zimmermann, “CERN Upgrade Plans”, EPS-HEP 09, Krakow, for a thorough discussion of luminosity factors.
If nb>156, must turn on crossing angle
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Maybe. Otherwise, push luminosity at
3.5 TeV
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Collimation Limits to Luminosity
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Target Performance in 2010
CommentEnerg
y(TeV)
Max Bunche
s
Protons/
bunch
% nom.Intensit
y
Min. *
(m)
Peak Lum.
(cm-2s-1)
Int. Lum.(pb-1)
Pilot Physics, Partial Squeeze, Gentle increase in bunch int.
3.5 43 3x1010 4 8.6x1029 .1-.2
3.5 43 5x1010 4 2.4x1030 ~1
Max. bunches with no angle 3.5 156 5x1010 2.5 2 1.7x1031 ~9
Push bunch intensity3.5 156 7x1010 3.4 2 3.4x1031 ~18
3.5 156 10x1010 4.8 2 6.9x1031 ~36
Increase energy to 4-5 TeV, as deemed prudent
Would aim to first provide a period of physics at the higher energy without crossing angle, this could be followed by a move to 50 ns with a limited number of bunches.
4-5 156 7x1010 3.4 2 4.9x1031 ~26
Introduce 50 ns bunch trains and crossing angle!
4-5 144 7x1010 3.1 2 4.4x1031 ~23
Push nb and Nb to limit of machine safety.
4-5 288 7x1010 6.2 2 8.8x1031 ~46
4-5 432 7x1010 9.4 2 1.3x1032 ~69
4-5 432 9x1010 11.5* 2 2.1x1032 ~110*limited by collimation system1/5/2010 53Eric Prebys - LHC Talk, Aspen 2010
Beyond 1032
Going beyond a few percent of the design luminosity depends on how far they are willing to push the existing collimation system. Won’t really know about this until after significant running
experience Getting anywhere near 1034 requires the Phase II collimation
system Details and schedule still being worked out Expect some guidance from Chamonix
Projection assuming Phase II collimation and Phase I upgrade done in 2013/2014 shutdown*
*R. Assmann, “Cassandra Talk”
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Getting to 7 TeV*
Note, at high field, max 2-3 quenches/day/sector Sectors can be done in parallel/day/sector (can be done in parallel)
No decision yet, but it will be a while*my summary of data from A. Verveij, talk at Chamonix, Jan. 2009
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LHC Upgrade path Initial operation
Ramp up to 1x1034 cm-2s-1
Phase I upgrade After ~2 years of operation (~2014) Replace 70 mm triplet quads with 120 mm quads * goes from 50->30 cm Linac4 to increase PSB injection energy to reduce space
charge effects Luminosity goes to 2-3x1034 cm-2s-1
Phase II upgrade Second half of next decade (nominally 2020) Luminosity goal: 1x1035
Details still under study New technology for larger aperture quads (Nb3Sn) crab cavities? Improved injector chain (PS2 + SPL)?
No major changes to optics or IR’s
Possible Significant Changes
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Acknowledgements and further reading This talk represents the work of an almost countless number of
people. I have incorporated significant material from:
Numerous talks given at the 2009 Chamonix session regarding “The Incident” http://tinyurl.com/Chamonix2009
Mirko Pojer’s talk at the US LHC Users’ Organization meeting at LBNL in September, 2009 http://tinyurl.com/usluo2009-pojer
Oliver Bruening’s talks at the LARP collaboration meeting in November http://tinyurl.com/cm13-bruening1 http://tinyurl.com/cm13-bruening2 (taken from Roger Bailey)
Commissioning status slides from Mike Lamont, and also significant material shown by Ralph Assmann and Frank Schmidt at the recent Tevatron Studies Workshop http://tinyurl.com/Tev-studies-workshop-2010
Luminosity considerations and upgrade plans, Frank Zimmermann’s talk to EPS-HEP, Krakow 2009 http://tinyurl.com/Zimmermann-Krakow
All things collimation (in particular, R. Assmann “Cassandra Talk”) http://lhc-collimation-project.web.cern.ch/1/5/2010 57Eric Prebys - LHC Talk, Aspen 2010
Staying informed Twitter feed (big news):
http://twitter.com/cern Commissioning log (more technical detail):
http://tinyurl.com/LHC-commissioning E-logbook (very technical, but good plots):
http://elogbook.cern.ch/eLogbook/eLogbook.jsp?lgbk=60 Only visible inside CERN network (if you have a CERN
account, you can use remote desktop or VPN from US).
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Decisions Q1 2009
Based on discussions at Chamonix 2009 Decided to warm up in 12 and 67 to replace faulty magnets Decided to warm up sector 56 in parallel for other reasons
Warming up means 3 weeks to get to 300K Repair work ELQA and other issues 6 weeks to get back to 2K
Q4 2008 Q1 2009
12 Cold Cold Warm
23 < 100K < 100K
34 Warm Warm
45 < 100K < 100K
56 Cold Cold Warm
67 Cold Cold Warm
78 Cold < 100K
81 Cold < 100K
Q4 2008 Q1 2009 Q2 2009 Q3 2009 Q4 2009
Sector 34 repair Restart
Talk by O. Bruning, LARP CM13 meeting, November, 20091/5/2010 60Eric Prebys - LHC Talk, Aspen 2010
Longitudinal displacements in damaged area
J.Ph. Tock
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Machine wide investigations Q2 2009 Electrical measurements while warm on sectors 12 34 56
67 Confirms new problem with the copper stabilizers
Non-invasive electrical measurements to show suspicious regions Several bad regions found
Open and make precise local electrical measurements Several bad stabilizers found (30µΩ to 50µΩ) and fixed
Measured other 4 sectors at 80K (noisy but gives limits)
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LHC Parameters and Options*
Parameter Symbol Initial Phase IPhase II Options
Early Sep.
Full Crab Low Emit.
Large Piw. Ang.
transverse emittance [mm] 3.75 3.75 3.75 3.75 1.0 3.75
protons per bunch Nb [1011] 1.15 1.7 1.7 1.7 1.7 4.9
bunch spacing Dt [ns] 25 25 25 25 25 50beam current I [A] 0.58 0.86 0.86 0.86 0.86 1.22
longitudinal profile Gauss Gauss Gauss Gauss Gauss Flat
rms bunch length z [cm] 7.55 7.55 7.55 7.55 7.55 11.8
beta* at IP1&5 * [m] 0.55 0.3 0.08 0.08 0.1 0.25
full crossing angle qc [mrad] 285 410 0 0 311 381
Piwinski parameter qcz/(2*x*) 0.64 1.26 0 0 3.2 2.0
peak luminosity L [1034 cm-2s-1] 1 3.0 14.0 14.0 16.3 11.9
peak events/crossing 19 57 266 266 310 452
initial lumi lifetime tL [h] 22 11 2.2 2.2 2.0 4.0
Luminous region l [cm] 4.5 3.3 5.3 5.3 1.6 4.2
*excerpted from F. Zimmermann, “LHC Upgrades”, EPS-HEP 09, Krakow, July 2009
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Limits of Phase I Collimation System*
Collimation at tightest settings throughout ramp
and squeeze
Somewhat more relaxed collimation settings
*Ralph Assmann, “Cassandra Talk”1/5/2010 64Eric Prebys - LHC Talk, Aspen 2010